The present invention relates to a substrate carrier for holding substrates, especially semiconductor wafers.
Substrate carriers for holding semiconductor wafers are known in the art. For example, with one such carrier, the wafer is held via a vacuum that is applied by a vacuum finger on a side of the wafer. With another form of a substrate carrier, a holding element is provided on the edge of the wafer. Although this substrate carrier can be put to many uses, there is a specialized application for which this type of substrate carrier is not suitable. Such a specialized use is, for example, a metal plating, especially a copper plating on one of the two surfaces of the wafer. With a metal plating of this type, the respective metal-containing treatment fluid is lead to the wafer surface to be plated, while a charge is applied between the wafer surface to be plated and an oppositely disposed anode. To produce this charge, it is necessary that the front side of the wafer to be plated be brought into electrical contact. An electrical contact on the backside of the wafer is therefore not possible, since the necessarily high current density for the plating on the front side of the wafer is not achievable by contacting the backside of the wafer without destroying any electronic structure in the wafer, for example transistors. Therefore, it is necessary to seal the surface of the wafer not to be treated against the copper in the treatment fluid, since metal in the area of the electronic structure can result in an undesired contamination. In particular, the electrical contacts for electrical contact of the front side of the wafer must also be protected from the electrolytes, since these electrolytes likewise can created an undesired metal layer.
The above-describe substrate carrier provides neither an electrical contact of the wafer surface to be treated nor a sealing of the non-treated surface against the treatment fluid.
In U.S. Pat. No. 5,429,733, a device for plating a wafer is disclosed in which the wafer is placed on a base portion with a central opening corresponding to the substrate shape, or as the case may be, on a seal disposed on the base portion. In order to securely hold the wafer, the wafer is pressed against the base portion or the seal with an inflatable balloon, which projects perpendicularly to the wafer surface. The seal comprises several undercuts in order to make possible an electrical contact with the surface of the wafer. Therefore, the undercut between the seal and the wafer is relatively large, which leads to a high damage to the margins or edges, since this area is sealed against any treatment. In addition, the interface between the seal and the wafer area creates a relatively neutral current when a fluid is flowed on the wafer, which leads to an non-homogeneous treatment of the wafer in this area.
U.S. Pat. No. 5,447,615 likewise shows a device in which the wafer is retained between a seal on a base portion and an inflatable balloon. An electrical contact of the wafer is accomplished through an opening in the seal portion which projects radially inward against the remaining seal.
In JP-A-7-211724, a device for plating a wafer is disclosed, in which the wafer is pressed by a substrate carrier against a seal lying on an upper edge of a treatment basin.
In contrast to the above described state of the art, the present invention addresses the task of providing a substrate carrier which permits, in a simple and reliable manner, sealing of a wafer surface to be treated while simultaneously allowing electrical contact of the surface to be treated, and one which allows a smaller undercut between the wafer and seal and a good flow of the treatment fluid in the area of the interface between the wafer and the seal.
The above task is resolved with the present invention which provides a substrate carrier for holding a substrate, especially a semiconductor wafer, having a first part and a second part, the second part having a central opening corresponding to the substrate shape, whereby the substrate is receivable between the first and second portions, and a peripheral seal is provided on the inner periphery of the second part and has at least one undercut. The peripheral seal on the inner periphery of the part having the central opening forms a radially inwardly extending boundary of the substrate carrier. On the basis of this peripheral seal, a good flow performance is achieved in the area of the interface between the wafer and the substrate when the substrate is washed with the treatment fluid. In addition, through the at least one undercut in the seal, an electrical contact of the surface of the wafer facing the central opening, outside of the surface of the wafer contacted with the treatment fluid, is possible.
Advantageously, the seal is formed by a sealing material applied to the inner periphery of the second part of the substrate carrier, which material is preferably welded or fused on in order to create a simple and inexpensive seal. Preferably, the sealing material overlaps a peripheral or edge area of the substrate in order to provide a reliable seal. Further, in this peripheral or edge area, an electrical contact of the substrate surface to be treated is made possible.
In a preferred form of the present invention, the seal has a sealing lip which is preferably constructed as a point or tip. The sealing lip, especially with a point or tip, provides the advantage of a good and defined seal and a defined transition between the wafer and the seal lip, which provides a uniform seal over time.
Preferably, the sealing lip is flush or joined with the inner periphery of the sealing material, that is, the sealing lip defines the most interior area of the sealing material in order to guarantee a uniform flow of the treatment fluid along the inner periphery of the sealing material.
In a particularly preferable embodiment of the present invention, the sealing lip is formed by a milling out of the sealing material. Upon applying sealing material to an inner periphery of the second part of the substrate carrier, in particular through fusing of the material, it is difficult to provide the necessary precision with regard to the shape and position of the sealing lip. For this reason, it is advantageous to mill out the sealing lip, or as the case may be, the entire shape of the seal first after applying the sealing material to the inner periphery of the second part of the substrate carrier, since then a higher precision of the shape and arrangement of the seal, in particular the sealing lip, can be achieved.
Preferably, the sealing material comprises polymeric material and is elastic. In this regard, the elasticity should not be too high so that the seal provides a sufficient pressure and a good seal against the wafer.
With another particularly advantageous embodiment of the present invention, an elastic element opposite the seal is provided on the first part of the substrate carrier, in order to create the necessary contact pressure and to balance the minimal elasticity of the sealing material. Through the elastic element, the substrate is pressed against the relatively rigid seal in order to prevent damage to the wafer from the seal. Therefore, the elastic element preferably lies opposite the sealing lip in order to sufficiently press the substrate in this area elastically against the point or tip of the sealing lip, thereby providing a good seal. For a simple and inexpensive solution, the elastic element is an O-ring. Preferably, the elastic element is held in a channel, especially a dovetail channel, in the first part of the substrate carrier to fix the position of the elastic element. The dovetail channel is particularly advantageous since, on the one hand, it offers a good fixing of the O-ring and, on the other hand, it allows a lateral extension of the O-ring.
According to a particularly preferred embodiment of the present invention, at least one centering element is provided on the second part of the substrate carrier. The centering element determines the position of the substrate with regard to the sealing, as well as the position of the first and second parts of the substrate carrier relative to one another, in order to provide a uniform operation of the seal. Preferably, the at least one centering element includes a bevel or slant along which a sliding centering can be performed. Preferably, several centering elements define an inner periphery which essentially corresponds to the outer periphery of the substrate in order to prevent lateral movement of the substrate during treatment, and to enable a simultaneous and precise placement of the seal. According to a preferred embodiment of the present invention, the centering element is constructed as a one-piece unit with the sealing material and is milled out from the sealing material, whereby an inexpensive manufacturing of the centering element is made possible. In addition, milling out of the sealing material provides the advantage that high precision can be maintained.
In another embodiment of the present invention, at least one centering element is provided in the first part of the substrate carrier in order to reliably determine the centering of the first and second parts of the substrate carrier. Therefore, the centering element on the first part of the substrate preferably has a bevel or slant, which lies opposite the bevel of the centering element on the second part and therefore is complementary thereto, in order to enable a simple way of centering the two parts. Preferably, the channel which receives the elastic element delimits the centering element.
In order to guarantee an electrical contact of the surface of the substrate, the substrate carrier has a contact assembly or arrangement. For contacting the front side of the substrate, on which the seal lies, the contact arrangement is preferably disposed on the second part of the substrate holder. Therefore, the contact arrangement projects into the area of the undercut in the seal in a particularly advantageous embodiment of the present invention.
For a good and reliable electrical contact of the substrate surface, the contact arrangement has at least one contact spring, which is biased in the direction of the substrate, and thereby reliably ensures good contact upon vibration or minimal movement of the substrate. Preferably, a plurality of contact springs are constructed by cut-outs in a ring-shaped contact member, in order to provide, in a simple and cost-effective manner, a uniform electrical contact over an outer periphery of the substrate.
With another preferred embodiment of the present invention, at least one chamber is formed between the first and second parts of the substrate carrier, and preferably serves to receive the contact arrangement. Preferably, the first chamber extends around the central opening of the substrate carrier, so that the first chamber is ring-shaped with a round substrate or angular with an angular substrate. In one embodiment, an inner periphery of the first chamber is sealed by the elastic element on the first part of the substrate carrier, by the substrate, and by the seal on the second part of the substrate carrier. An outer periphery of the first chamber is sealed by at least one sealing element on the first and/or second parts of the substrate carrier. In this regard, the sealing element for a good and cost-effective sealing is an O-ring.
According to a further preferred embodiment of the present invention, at least one second chamber is provided between the first and second parts of the substrate carrier. The second chamber preferably extends around the first chamber, and includes at least one sealing element on the first and/or second parts of the substrate carrier for sealing the second chamber. Advantageously, two sealing elements for sealing the second chamber are provided, which preferably are O-rings.
For holding together the first and second parts of the substrate holder, preferably a device for applying a vacuum to the first and/or second chamber is provided. With a vacuum, the first and second parts can be held against one another in a simple manner and by releasing the vacuum, the first and second parts can be easily separated from one another, in order, for example, to grasp the substrate held between the two parts.
To stabilize the sealing lip, the first chamber can be advantageously filled with a fluid, for example N2, in order to create a counter pressure to the pressure of the treatment fluid acting on the sealing lip. In order to prevent a bending or deformation of the substrate during treatment, a substrate support surface is provided on the first portion of the substrate carrier for the side of the substrate which is not to be treated, which support surface essentially has the same shape as the substrate.
The first and second parts of the substrate carrier preferably each have a metal body, in order to provide the substrate carrier with the necessary rigidity and strength. Each respective metal body is provided with a coating of polymeric material to prevent contact between metal-based contaminants and the substrate, or, as the case may be, to prevent contact between the metal-attaching treatment fluid and the metal body. Preferably, the coatings have areas with varying thicknesses, in order to allow for the forming of the above-described channels, chambers and the like.